This application claims a priority based on Japanese Patent Application No. 2000-157922 filed on May 29, 2000, the entire contents of which are incorporated herein by reference for all purposes.
The present invention relates to an optical signal switching apparatus, and particularly to an optical signal switching apparatus having an optical protection function.
First, structures for realizing an optical protection function, i.e., the optical 1+1 switching structure and the optical 1:1 switching structure will be described (See Japanese Unexamined Patent Laid-Open No. 6-244796 and Tong-Ho Wu, xe2x80x9cFiber Network Service Survivabilityxe2x80x9d, Artech House (1992), pp. 88-93).
FIG. 5 is a block diagram showing the conventional optical 1+1 switching structure. The optical 1+1 switching structure includes an optical transmitter 1001, an optical coupler (splitter) 1002, a working optical fiber 1003, a protection optical fiber 1004, an optical switch 1005, and an optical receiver 1006. On the transmitting side, an optical signal outputted from the optical transmitter 1001 is split by the optical coupler (splitter) 1002, and outputted to the working and protection optical fibers 1003 and 1004. On the receiving side, either of the working and protection optical fibers 1003 and 1004 is selected by the optical switch 1005, and the optical signal is received by the optical receiver 1006.
FIG. 6 shows a block diagram showing the conventional optical 1:1 switching structure. The optical 1:1 switching structure includes a working optical transmitter 1011, a protection optical transmitter 1021, an optical switch 1012, a working optical fiber 1013, a protection optical fiber 1014, an optical switch 1015, a working optical receiver 1016, and a protection optical receiver 1026. On the working transmitting side, an optical signal (data) outputted from the working optical transmitter 1011 is switched by the optical switch 1012, and usually outputted to the working optical fiber 1013. On the working receiving side, the working optical fiber 1013 is selected by the optical switch 1015, and the optical signal is received by the working optical receiver 1016. On the other hand, also in the protection system, an optical signal (extra data) outputted from the protection optical transmitter 1021 is switched by the optical switch 1012, and usually outputted to the protection optical fiber 1014. The protection optical fiber 1014 is selected by the optical switch 1015, and the optical signal is received by the protection optical receiver 1026.
Further, in the case of trouble with the working optical fiber 1013, the optical switches 1012 and 1015 are switched so that data outputted from the working optical transmitter 1011 is received by the working optical receiver 1016 through the protection optical fiber 1014. In any case, the optical receivers 1006, 1016 and 1026 receive an optical signal and convert it to an electric signal.
In the above-described techniques, when the optical 1+1 switching structure is changed (expanded) to the optical 1:1 switching structure, it is necessary to replace the optical coupler (splitter) with the optical switch. Further, these switching structures tend to generate rapid fluctuation of optical power, at the time of switching optical signals (changeover of the optical switches). In particular, when an optical amplifier is connected in a subsequent stage to an optical switch, there may arise (a) excessive optical output (optical surge), or (b) effects (disturbances) on optical signals of other wavelengths at the time of general amplification of multiple wavelengths.
In consideration of the above problems, the present invention provides an optical signal switching apparatus whose hardware can be commonly used for the 1+1 switching structure (splitting on the sending side and switching on the receiving side) and the 1:1 switching structure (switching on the sending side and switching on the receiving side). Further, the present invention provides an optical signal switching apparatus that has sending-side and receiving side switches having the same structure, and thus is suitable for unifying and integrating sending and receiving components. Further, conventionally, an optical coupler should be replaced with an optical switch, and accordingly in-service transformation is difficult. On the other hand, according to the present invention, in-service transformation from the 1+1 switching structure to the 1:1 switching structure and in-service transformation from the 1:1 switching structure to the 1+1 switching structure are possible.
Further, according to the present invention, the control circuits are provided, and accordingly, it is possible to suppress rapid optical power fluctuation accompanying optical signal switching. In particular, the present invention can suppress (a) cause of excessive optical output (generation of optical surge), (b) effect (disturbance) on optical signals of other wavelengths at the time of general amplification of multiple wavelengths, etc. in an optical amplifier.
Further, conventionally, when generation of optical signal interruption (LOS) or the like is detected at the time of switching from working system to protection system, malfunction can occur. However, according to the present invention, switching can be performed without generating optical signal interruption.
In the present invention, in particular, a variable (coupling ratio) optical coupler is applied to a switch of an optical signal switching apparatus. At the time of the 1+1 switching structure, the sending side is made to have a splitting structure (coupling ratio=50%:50%) and the receiving side is made to have a switching structure (coupling ratio=100%:0%, or 0%:100%). At the time of the 1:1 switching structure, the sending side is made to have a switching structure (coupling ratio=100%:0%, or 0%:100%) and the receiving side is made to have a switching structure (coupling ratio=100%:0%, or 0%:100%).
Further, the present invention can realize an optical signal switching function without rapid optical power fluctuation, by combining a variable (coupling ratio) optical coupler with a control circuit that gradually (continuously) controls the coupling ratio of the coupler.